Apparatus for inductively surface hardening workpieces of at least approximately axially symmetrical shape

ABSTRACT

An apparatus for inductively surface hardening a workpiece having two heating conductors extending on each side of the workpiece parallel to the workpiece axis and a cross conductor at one end of the workpiece completing the conductor loop. According to the invention of this application, a further conductor is provided about the workpiece with surfaces extending parallel to and slightly separated from inner surfaces of the cross conductor ground part of the circumference and around the workpiece for the rest of the circumference so that current flow is induced in the further conductor. The further conductor is preferably mounted for axial movement so that the distance between a stop holding one end of the workpiece and the further conductor remains the same.

United States Patent 1 1 3,739,131 Reinke 1 June 12, 1973 APPARATUS FOR INDUCTIVELY 3,441,701 4/1969 Seuleu et al. 219/10.79

SURFACEHARDENING WORKPIECES 0F 2,383,992 9/1945 Sherman 2l9/l0.79 X

AT LEAST APPROXIMATELY AXIALLY SYMMETRICAL SHAPE Inventor: Friedhelm Reinke, Remscheid,

Germany Foreign Application Priority Data Sept. 23, 1971 Germany P 21 47 518.3

US. Cl. 219/10.79, 219/lO.43 Int. Cl. H05b 5/02 Field of Search 219/10.79, 10.41,

219/l0.43; 266/4 E, 5 E

References Cited UNITED STATES PATENTS 8/1972 Reinke 219/l0.43

Primary Examiner.l. V. Truhe Assistant Examiner-B. A. Reynolds Attorney-John W. Malley, Paul N. Kokulis and James R. Longacre et al.

[57] ABSTRACT An apparatus for inductively surface hardening a workpiece having two heating conductors extending on each side of the workpiece parallel to the workpiece axis and a cross conductor at one end of the workpiece completing the conductor loop. According to the invention of this application, a further conductor is provided about the workpiece with surfaces extending parallel to and slightly separated from inner surfaces of the cross conductor ground part of the circumference and around the workpiece for the rest of the circumference so that current fiow is induced in the further conductor. The further conductor is preferably mounted for axial movement so that the distance between a stop holding one end of the workpiece and the further conductor remains the same.

10 Claims, 3 Drawing Figures PAIENIED JUN 1 2 1973 saw 1 or 2 APPARATUS FOR INDUCTIVELY SURFACE-HARDENING WORKPIECES F AT LEAST APPROXIMATELY AXIALLY SYMMETRICAL SHAPE The invention relates to apparatus for inductively surface-hardening at least approximately axially symmetrical workpieces by the rotary method, particularly by using an inductor consisting of two heating conductors extending on each side of the workpiece in the general direction of the workpiece axis and connected near one of the workpiece ends by a connecting conductor which extends crosswise of the workpiece axis and completes the heating conductor loop, this cross conductor having a surface area with faces extending at least nearly parallel to the workpiece axis.

Hardening machines equipped with inductors of the above described type have been described for instance in the published specification of German Patent application No. 1,583,331. With particular advantage they can be used for instance for surface-hardening the rear axle shafts of motor vehicles, which require a hardened zone having as uniform a thickness as possible. Such rear axle shafts are usually provided at one end with a flange and at the other end with external splines. The hardened layer on the shaft surface, which extends at one end across the fillet up part of the flange, is desired 1 at the other end to involve as much as possible of the splines but, as has been found by experience, it should not extend to the free end face of the shaft because if this were so, cracks would appear between the hardened surface layer and the core material. For achieving workpieces having optimum properties it is, therefore, important that the hardened zone should always terminate at a precisely predetermined point of the splined end of the shaft.

In a conventional inductor, such as that described with reference to FIG. 1 in the above mentioned German published specification No. 1,583,331, the connecting cross conductor between the two heating conductors which extend on each side of the workpiece in predetermined axial direction consists of a semicircular conducting bridge, which arches above the workpiece surface and forms part of the heating conductor of the inductor. wherein has been found in practice that, when using the conventional inductor, any variation of the current in the heating conductor and/or in the heating-up time for the purpose of changing the depth of the hardened layer will also involve an axial shift of the end of the hardened layer in the splined end of the shaft. Since it is desired that the hardened layer at this end should not extend beyond a given point towards the free end of the shaft it is the usual practice to allow for variations in the depth of the hardened layer by so designing the inductor in length that, for a given average depth of the hardened zone, this zone will end a given safety distance short of the desirable optimum point. The greater the tolerances in overall length of the workpiece, the longer this distance must be and frequently this is not very critical in the case of vehicle rear axles.

It is, therefore, the object of the present invention to contrive apparatus for inductively surface-hardening workpieces that are at least approximately axially symmetrical, by the rotary method, using an inductor consisting of two heating conductors extending on each sideof the workpiece in the general direction of the workpiece axis and being connected near one of the workpiece ends by a connecting conductor which extends crosswise of the workpiece axis and completes the heating conductor loop, in such a way that the apparatus permits the position of the end of the hardened zone to be adjusted.

According to this invention, this is achieved in apparatus of the specified kind by an inductor which in addition to its heating conductor loop also includes a conductor which forms a the and which has a surface area comprising faces which are at least nearly parallel to the workpiece axis, and which extend, in a manner leaving a narrow circumferential clearance gap, around part of the circumference of the closed loop conductor, in close proximity with the corresponding axially parallel faces of the cross conductor, and around another part of its circumference, in close proximity with the end of the workpiece surface that is to be hardened, this closed conductor loop being axially adjustable in relation to the heating conductor loop for the purpose of varying the effective length at the end of the workpiece that will be heated.

According to one aspectof this invention, the closed conductor loop may be axially movably mounted and energy storage means may be provided urging the closed conductor loop towards the workpiece end, as well as a mounting element for engaging said workpiece end and in conventional manner serving to impart rotation to the workpiece about its axis, this mounting element being axially adjustable connected to stop meant for displacing the closed conductor loop against the thrust of said energy storage means into a fixed predetermined position in relation to the work piece end.

In an alternative embodiment of the invention a conventional mounting element which engages end and im parts rotation to along workpiece may be connected to the axially movable closed conductor loop and thereby, during the workpiece mounting process, axially locate the same in a fixed predetermined position in relation to said workpiece end.

According to another feature of the invention axially parallel faces-of the cross conductor and a terminal region of the workpiece surface that is to be hardened together define an opening in which the closed conductor loop is axially adjustable.

Moreover, according to yet another feature of the inventon, the dimensions in the direction of the workpiece axis of the mutually facing axially parallel surface areas of the cross conductor and of the closed conductor loop differ in such manner that, notwithstanding variations in the positions occupied by the closed conductor loop during inductive heating, the mutual overlap between the surface areas and hence the degree of inductive coupling between the cross-conductor and the closed conductor loop will remain constant.

Finally, in a useful embodiment of the invention corresponding portions of the cross conductor and of the closed conductor loop and/or the portion of the closed conductor loop which faces the workpiece surface may be provided with magnetic yoke cores or laminated magnetic yokes.

The invention will be hereinafter more particularly described with reference to the accompanying drawings in which:

FIG. 1 shows a side view of one embodiment of this invention heating a workpiece;

FIG. 2 shows a front view of the embodiment of FIG.

FIG. 3 shows a sectional view through l-I in FIG. 2. In FIGS. 1 and 2 the region 1 at the end of the workpiece that is to be hardened, the spindle end 2 upon which the workpiece is mounted and a portion of the inductor corresponding to the length of this region are shown in two relatively perpendicular sections. End 1 shown in the drawings of the relatively elongated workpiece, which may be the rear axle shaft of a vehicle, is provided with external splines in which the hardened zone is to terminate a given distance from the end of the shaft. The heating conductor loop of the inductor comprises two heating conductors 4 extending in the direction of the workpiece axis 3. These two conductors are cross connected near the end of the workpiece by a conductor 5 which extends across the workpiece axis, and which in the illustrated example comprises two separate branches 5' and 5" for completing the loop and providing connections 6 and 7 t inductor terminals (not shown in the drawing).

Cross conductor has a surface 8 which is parallel to the workpiece axis 3 and so shaped that this surface in conjunction with a portion 9 of the workpiece surface that is to be hardened defines an opening or channel (FIG. 2). This channel contains a conductor 10 which closes upon itself, and which also comprises a surface 11 which is parallel to the workpiece axis, and which conforms with the shape of the axially parallel surface 8 of the cross conductor 5 and of the end portion 9 of the workpiece that is to be hardened, in such manner that a narrow all-around clearance gap remains. The heating conductor loop and the closed conductor loop 10 are preferably made of copper tubes of rectangular cross section and in operation a coolant circulates through their interiors. In FIG. 2 the connections 12 for the coolant of the closed conductor loop 10 are shown.

For improving mutual inductive coupling between the cross conductor 5 and the closed conductor loop 10, magnetic yoke cores or laminated yokes 13 and 14 are attached to corresponding sections of these conductors as shown in FIG. 3.

The inductor current, which during inductive heating of the workpiece flows through the cross conductor 5, induces a current in the closed conductor loop 10 and this induced current effects the inductive heating of the end 9 of the workpiece. For the purpose of concentrating the field in this part 9 of the workpiece, closed conductor loop 10, as is otherwise conventional in inductors, is armed with a laminated magnetic yoke 15 in this region.

The manner in which the closed conductor loop 10 is supported and the arrangements made for adjusting the same for the purpose of precisely controlling the end of the hardened zone will now be described with reference to FIG. 3 which is a section of the arrangement taken on the line I-l in FIG. 2.

Closed conductor loop 10 is attached to a holder 16 made of electrically insulating material and mounted slidably in the axial direction on two pins 19 secured to an inductor bracket 18. Two compression springs 20 which serve as energy storage means are likewise mounted on the pins 19 and bear at one end against the inductor bracket 18, urging holder 16, together with closed inductor loop 10, in the direction indicated by an arrow 21. Spindle 2 of which the rotating center 22 engages the end 23 of the workpiece carries a stop 24 which is axially shiftable clamped to the spindle.

During the process of mounting the workpiece, which comprises advancing the spindle 2 and its stop 24 in the direction indicated by an arrow 25 towards the workpiece, the abutment face of the stop 24 displaces the holder 16 and the closed conductor loop 10 against the resistance of the compression springs 20 in such a way that, irrespectively of differences in the overall length of the workpiece, closed conductor loop 10 will be in a position which is precisely determined in relation to the end 23 of the workpiece, so that the heating zone generating the end of the hardened zone by inductive heating will also terminate at an exactly predetermined distance from the end 23 of the workpiece.

In order to ensure that the inductive coupling between the cross conductor 5 and the closed conductor loop 10 is constant, the width a of the cross conductor 5, measured in the axial direction of the workpiece, exceeds the width b of the closed conductor loop 10 by at least the length of its axial adjustability range so that, irrespectively of the final position of the closed conductor loop 10, its entire peripheral face will always be overlapped by the corresponding face of the cross conductor 5.

Provided the movements the workpiece performs in the hardening machine are not thereby obstructed, a simpler embodiment of the arrangement according to the invention consists in directly attaching the closed conductor loop, by suitable holding means in an axially adjustable manner, directly to the mounting element of the work, such as a spindle, so that it will necessarily have been moved into the correct prescribed position in relation to the end of the workpiece when the mounting element grips the workpiece end. This variant may be used with advantage when the mounting, inductive heating, quenching and final release of the workpiece all take place at one and the same station in the hardening machine.

In a different embodiment of the proposed arrangement the closed conductor loop provided with a suitable holder is axially adjustably attached to the support means carrying the inductor. This modification will be particularly useful when the nature of the mounting device ensures that the contemplated end of the mounted workpiece will always occupy exactly the same position in relation to the inductor. Many other changes and modifications in the above described embodiment can, of course, be made without departing from the scope of the invention. Accordingly, that scope is intended to be limited only by the scope of the appended claims.

What is claimed is:

1. In an apparatus for inductively surface-hardening at least approximately axially symmetrical workpieces by the rotary method, having an inductor with two heating conductors extending on each side of the workpiece in the general direction of the workpiece axis and connected near one of the workpiece ends by a connecting conductor which extends cross wise of the workpiece axis and completes the heating conductor loop, said cross conductor having a surface with faces extending at least nearly parallel to the workpiece axis, the improvement including a further conductor forming a closed loop, and having a surface with faces which are at least nearly parallel to the workpiece axis and which extend in a manner leaving a narrow circumferential clearance gap, around part of the circumference of the closed loop conductor, in close proximity with the corresponding axially parallel faces of the cross conductor and, around another part of its circumference, in close proximity with the end of the workpiece surface that is to be hardened, and means for axially adjusting said closed conductor loop in relation to said heating conductor loop to vary the effective length at the end of the workpiece that is to be heated.

2. In an apparatus according to claim 1, the further improvement wherein said closed conductor loop is axially movably mounted and energy stored means are provided urging the closed conductor loop towards the workpiece end as well as a mounting element for engaging said workpiece end and in conventional manner serving to impart rotation to the workpiece about its axis, said mounting element being axially adjustably connected to stop means adapted to displace the closed conductor loop against the thrust of the said energy storage means into a fixed predetermined position in relation to said workpiece end.

3. In an apparatus according to claim 2, the further improvement whrein a mounting element of basically conventional kind is disposed for engaging said workpiece end and for imparting rotation thereto, said mounting element being connected to the axially adjustably movable closed conductor loop and thereby during the workpiece mounting process axially locating the same in a fixed predetermined position in relation to said workpiece end.

4. In an apparatus according to claim 3, the further improvement wherein axially parallel faces of the cross conductor and a terminal region of the workpiece surface that is to be hardened together define an opening in which the closed conductor loop is axially adjustable.

5. In an apparatus according to claim 4, the further improvement wherein the dimensions in the direction of the workpiece axis of the mutually facing axially parallel surface areas of the cross conductor and of the closed conductor loop differ in such manner that, notwithstanding variations in the positions occupied by the closed conductor loop during inductive heating the mutual overlap between the said surface areas and hence the degree of inductive coupling between the cross conductor and the closed conductor loop remains constant.

6. In an apparatus according to claim 5, the further improvement wherein corresponding portions of the cross conductor and of the closed conductor loop of the inductor are provided with magnetic yoke cores or laminated magnetic yokes.

7. In an apparatus according to claim 6, the further improvement wherein the portion of the closed conductor loop of t he inductor which faces the workpiece surface is provided with magnetic yoke cores or laminated magnetic yokes.

8. An apparatus for inductively surface hardening a workpiece comprising:

a pair of heating conductors extending on each side of said workpiece substantially parallel to the workpiece axis,

a cross conductor extending substantially crosswise of the workpiece axis and connecting said pair of conductors together to form a conductor loop,

further conductor mounted between said cross conductor and said workpiece so that a current is induced in said further conductor which in turn induces a heating current in said workpiece, and

means for mounting said further conductor so that said further conductor is axially movable along said workpiece.

9. An apparatus as in claim 8, further including stop means for holding an end of said workpiece including means for engaging said mounting means for urging said mounting means along said workpiece axis.

10. An apparatus as in claim 9, wherein said mounting means includes a shaft, means for holding said further conductor and slidable along said shaft including a portion for receiving said engaging means so that said engaging means urges said holding means a ong said shaft, a member connecting said cross conductor to said shaft, and a spring mounted on said shaft urging said holding means toward said engaging means. 

1. In an apparatus for inductively surface-hardening at least approximately axially symmetrical workpieces by the rotary method, having an inductor with two heating conductors extending on each side of the workpiece in the general direction of the workpiece axis and connected near one of the workpiece ends by a connecting conductor which extends cross wise of the workpiece axis and completes the heating conductor loop, said cross conductor having a surface with faces extending at least nearly parallel to the workpiece axis, the improvement including a further conductor forming a closed loop, and having a surface with faces which are at least nearly parallel to the workpiece axis and which extend in a manner leaving a narrow circumferential clearance gap, around part of the circumference of the closed loop conductor, in close proximity with the corresponding axially parallel faces of the cross conductor and, around another part of its circumference, in close proximity with the end of the workpiece surface that is to be hardened, and means for axially adjusting said closed conductor loop in relation to said heating conductor loop to vary the effective length at the end of the workpiece that is to be heated.
 2. In an apparatus according to claim 1, the further improvement wherein said closed conductor loop is axially movably mounted and energy stored means are provided urging the closed conductor loop towards the workpiece end as well as a mounting element for engaging said workpiece end and in conventional manner serving to impart rotation to the workpiece about its axis, said mounting element being axially adjustably connected to stop means adapted to displace the closed conductor loop against the thrust of the said energy storage means into a fixed prederermined position in relation to said workpiece end.
 3. In an apparatus according to claim 2, the further improvement whrein a mountiNg element of basically conventional kind is disposed for engaging said workpiece end and for imparting rotation thereto, said mounting element being connected to the axially adjustably movable closed conductor loop and thereby during the workpiece mounting process axially locating the same in a fixed predetermined position in relation to said workpiece end.
 4. In an apparatus according to claim 3, the further improvement wherein axially parallel faces of the cross conductor and a terminal region of the workpiece surface that is to be hardened together define an opening in which the closed conductor loop is axially adjustable.
 5. In an apparatus according to claim 4, the further improvement wherein the dimensions in the direction of the workpiece axis of the mutually facing axially parallel surface areas of the cross conductor and of the closed conductor loop differ in such manner that, notwithstanding variations in the positions occupied by the closed conductor loop during inductive heating the mutual overlap between the said surface areas and hence the degree of inductive coupling between the cross conductor and the closed conductor loop remains constant.
 6. In an apparatus according to claim 5, the further improvement wherein corresponding portions of the cross conductor and of the closed conductor loop of the inductor are provided with magnetic yoke cores or laminated magnetic yokes.
 7. In an apparatus according to claim 6, the further improvement wherein the portion of the closed conductor loop of t he inductor which faces the workpiece surface is provided with magnetic yoke cores or laminated magnetic yokes.
 8. An apparatus for inductively surface hardening a workpiece comprising: a pair of heating conductors extending on each side of said workpiece substantially parallel to the workpiece axis, a cross conductor extending substantially crosswise of the workpiece axis and connecting said pair of conductors together to form a conductor loop, further conductor mounted between said cross conductor and said workpiece so that a current is induced in said further conductor which in turn induces a heating current in said workpiece, and means for mounting said further conductor so that said further conductor is axially movable along said workpiece.
 9. An apparatus as in claim 8, further including stop means for holding an end of said workpiece including means for engaging said mounting means for urging said mounting means along said workpiece axis.
 10. An apparatus as in claim 9, wherein said mounting means includes a shaft, means for holding said further conductor and slidable along said shaft including a portion for receiving said engaging means so that said engaging means urges said holding means a ong said shaft, a member connecting said cross conductor to said shaft, and a spring mounted on said shaft urging said holding means toward said engaging means. 